The present invention relates to a method of desulphurizing and cracking hydrocarbons by subjecting the hydrocarbons which have been admixed with certain key components to microwave energy. Through the judicious choice of additives and the use of microwave power, hydrocarbons high in sulphur content and high in molecular weight can be made into useful products which can be burned cleanly and efficiently as a fuel oil.
This invention relates to the high frequency treatment of hydrocarbons, more particularly, to the desulphurization and upgrading of fuel oils. Hydrocracking processes for the conversion of heavy hydrocarbon oils to naphtha and diesel fuel are well known. The most appropriate uses of those products are as sources of energy. However, high sulphur content in fuels in the form of organic sulphur compounds creates serious environmental problems, the removal of which requires very costly equipment. It is also highly desirable to provide a hydrocracking process, which provides for the simultaneous cracking and removal of sulphur in forms other than SO2. Further, the presence of nitrogen and oxygen in fuel oils are also undesirable as nitrogen is converted into nitrogen oxide gases, whose release to the atmosphere is regulated. In addition, nitrogen poisons catalysts. The removal of oxygen from feedstock upgrades the fuel by increasing its heating value.
The most commonly used process to reduce sulphur levels in hydrocracked feedstock is hydrodesulphurization. This is a catalytic process, taking place at high temperatures and hydrogen pressure. For example, Baird, Jr. et al. described a hydrodesulphurization process in U.S. Pat. No. 4,087,348 where the heavy hydrocarbon feedstock is contacted with hydrogen and a reagent selected from alkaline earth metal hydrides, oxides and mixtures thereof. However, that process is carried out at temperatures in the range of 700xc2x0 F. to 1500xc2x0 F. which induces caking and high partial pressures ranging from 1500 to 3000 psi.
Kirkbridge teaches, in U.S. Pat. No. 4,234,402, that the sulphur content of crude petroleum can be reduced by subjecting a mixture of the crude petroleum and hydrogen gas to microwave energy. In U.S. Pat. No. 4,279,722, Kirkbridge describes use of microwave energy in petroleum refinery operations which requires a platinum catalyst and high hydrogen pressures of, for example, 200-2,000 psi.
The process for removing sulphur from coal was described in U.S. Pat. No. 4,148,614. Sulphur content was taught to be reduced by drying coal particles and subjecting a mixture thereof to hydrogen under the influence of microwave energy. Wan et al. disclose in U.S. Pat. No. 4,545,879 employing microwave heating to desulphurize pulverized petroleum pitch using para- or ferromagnetic catalysts. The required amount of catalyst was taught to be the same as the amount of treated feedstock. Maximum removal of sulphur was shown to be 70%.
All of the above-noted processes required the presence of hydrogen gas at high pressure. Sulphur content in the hydrocarbon feedstock after reduction was from 200 to 1500 ppm, noting that sulphur and hydrogen were removed in the form of hydrogen sulfide which required further processing.
It is thus an object of the present invention to provide a process for creating useable fuel oil capable of being burned as a clean and efficient source of energy from hydrocarbon stock which would otherwise be relatively unusable.
It is yet a further object of the present invention to provide an efficient method of reducing the sulphur content of hydrocarbon fuel and to crack the hydrocarbon fuel to lower its average molecular weight in order to provide a relatively clean burning and useful commercial product.
These and further objects of the present invention will be more readily appreciated when considering the following disclosure and appended claims.
The present invention is directed to a method of desulphurizing and cracking fuel oil comprising first admixing the fuel oil with a sensitizer and solid source of hydrogen to form an admixture followed by subjecting the admixture to microwave energy. Preferably, the fuel oil further contains a catalyst and desulphurizing additive such that upon being subject to microwave energy, the cracked product is reduced in molecular weight and provided with a lower sulphur content such as to provide a commercially viable product which can be cleanly burned as a source of energy.
According to the preferred embodiment of the present invention it has been discovered that hydrocracking and desulphurization of the hydrocarbon oils can be carried out by mixing hydrocarbon feedstock with para-or ferromagnetic catalysts and sensitizers, desulphurizing agents and in-situ solid sources of hydrogen and subjecting this mixture, in the absence of hydrogen gas, to microwave irradiation. Micro-discharges are generated thereby upgrading the oils while releasing and separating chemically bound organic sulphur from the hydrocarbon feedstock as sulphur-contained solid and gaseous inorganic compounds, nitrogen as ammonia and oxygen as water.
In the present process, a mixture of hydrocarbon feedstock, sensitizer, catalyst, desulphurizing additives and in-situ solid hydrogen sources are subjected to the influence of microwave energy. Sensitizers are selected as materials that strongly absorb microwave radiation and subsequently transfer the energy required to initiate certain desired chemical reactions. Catalysts allow for the localization of temperature increases creating conditions for the generation of micro-discharges near the surfaces of the sensitizer when the processed mixture is irradiated with microwaves. The micro-discharges represent a highly non-equilibrium system of ionized molecules and electrons where the kinetic energy (xe2x80x9ctemperaturexe2x80x9d) of the electrons is significantly higher than the average temperature of the system. Without being bound by any particular theory, it is believed that the electron energy is sufficient to break the chemical bonds in the molecules forming free radicals. As a result, the hydrocarbon oil is upgraded. At the same time the sulphur, nitrogen and oxygen atoms, as well as the in-situ solid hydrogen source are activated in the microwave reactor. Sulphur reacts with hydrogen and oxygen, as well as with desulphurizing additives to form inorganic salts such as sulfates, sulfites and sulfides. Specifically, sulphur is converting from its organic to an inorganic form as a result of its exposure to microwave irradiation. Sulfides, sulfites, hydrogen and hydrogen sulfide are formed in reactions such as:
Snorganic+2NaHxe2x86x92Na2Sn+H2 
Snorganic+2m NaHxe2x86x92m Na2S(n/mxe2x88x921)+m H2S 
Snorganic+4NaOHxe2x86x92Na2Snnxe2x88x921+Na2SO3+H2O+H2 
Hydrogen sulfide is converting into sulfate in the reactor:
H2S+2 NaOH+O2xe2x86x92Na2SO4+H2 
Oxygen forms water with hydrogen. Activated nitrogen reacts with hydrogen and water to form ammonia. The hydrocarbon fuel source, which is purified by the removal of sulphur, nitrogen and oxygen is upgraded in its physical and chemical properties in the form of a liquid and a gas. The fuel source is separated from its solid inorganic salts, which contained sulphur, nitrogen and oxygen by evaporation from the microwave reactor and can be condensed through the use of a heat exchanger. The process can be carried out at atmospheric pressure which provides for hydrocracking and in-situ desulphurization while avoiding the use of hydrogen gas.
As noted above, the wave energy used in the present process is in the microwave range. The equipment for generating microwave energy for use herein is well known in the art. For example, reference is made to applicant""s previously issued U.S. Pat. No. 6,184,427, the disclosure of which is incorporated by reference herein.
The sensitizers used in the present process are materials which strongly absorb microwave energy and are suitable to play the role of xe2x80x9cenergy converterxe2x80x9d. Suitable sensitizers again are disclosed in U.S. Pat. No. 6,184,427 and include activated carbon and metal oxides such as NiO, CuO, Fe3O4, MnO2, Co2O3, and WO3. The concentration range for the proposed sensitizers is preferably approximately 0.5-20 wt % based upon the weight of the fuel oil being processed.
The catalysts used in present process are also disclosed in U.S. Pat. No. 6,184,427 and can be a metal powder such as a para- or ferromagnetic material, preferably a metal powder, such as iron, copper, or nickel. The concentration range is preferably approximately 0.5-10 wt % based upon the weight of the fuel oil being processed.
As noted above, desulphurizing additives are used to eliminate sulphur contamination in the final fuel oil product. They may consist of granulated limestone and other forms of CaCO3, calcite (CaO), magnesite (MgO), dolomite (MgOxe2x80x94CaO), sodium hydroxide (NaOH), potassium hydroxide (KOH) and sodium bicarbonate (NaHCO3). The preferred concentration range of the desulphurizing additive is preferably approximately 0.5-25 wt % based upon the weight of the fuel oil being processed.
An in-situ solid source of hydrogen is used to provide hydrogen atoms for hydrocracking and desulphurization without the direct use of hydrogen gas. This solid source of hydrogen may be derived from various hydrides, such as sodium borohydride (NaBH4), titanium hydride (TiH2), potassium hydride (KH), copper hydride (CuH), zinc hydride (ZnH), sodium hydride (NaH), chromium hydride (CrH) and nickel hydride (NiH 0.5). The concentration range for this component is preferably approximately 0.5-20 wt % based upon the weight of the fuel oil being processed.